Method of manufacturing fire detector and like elements



Jan. 31, 1950 M. F. PETERS METHOD OF MANUFACTURING FIRE DETECTOR AND LIKE ELEMENTS Filed Jan. 14, 1948 INVENTOR. Maw/z if f/ EMWF;

w 2;??? Fi a??? 5% do twfma pwu/ Patented Jan. 31, 1950 METHOD OF MANUFACTURING FIRE DETECTOR AND LIKE ELEMENTS Melville F. Peters, Newark, N. J assignor to Petcar Research Corporation, Newark, N. J., a corporation of New Jersey Application January 14, 1948, Serial No. 2,344

Claims.

This invention relates broadly to the manufacture of flexible cables of the general type comprising one or more continuous wires surrounded by a covering which may be electrically insulating or have other desired qualities.

In my co-pending application Serial No. 90,881, I have disclosed and claimed a continuous wire cable of new and improved type and construction which is adapted and intended for use in fire detector systems. This cable comprises two spaced, continuous, electrically conductive wires which are surrounded and held in spaced, parallel relation by beads which are spaced along the conductors and are fused to them. My invention is of great utility in the manufacture of such a cable but is of equal utility in the manufacture of other continuous covered wire cables generally, regardless of the number of conductors or the use to which the cable is to be put. The primary result of the invention has been to provide a method of manufacturing cables of the described type and construction which is feasible and practical from the engineering, manufacturing and economic standpoints.

As stated above, the method provided by this invention is of great utility in the manufacture of fire detector elements of the continuous cable type particularly described and claimed in my co-pending application When intended for use in such fire detection systems the beads of the cable, which surround the two wires and hold them in spaced relation, are formed of so-called thermistor material which is electrically insulating at normal temperatures and becomes electrically conductive at some predetermined temperature, thus completing an electric circuit through the wires causing some operation, such as the energization of a signal, to be performed. While this invention is of general utility in the manufacture of continuous wire cables of all types and regardless of the purpose for which the cable is to be used, it will be described in this application in connection with the manufacture of a cable having beads of thermistor material and adapted and intended for use in a fire detection system.

The method of manufacture provided by this invention consists, in general. in forming around one or more continuous, parallel wires, which may be electrically conductive, a solid cylinder of oo- 2, hesive material which on heating becomes fused to the wire or wires and shrinks longitudinally thereof to form separate, spaced beads along the length of the wire or wires.

The steps in a preferred method according to the invention are illustrated in the drawings which, like the specification, are only illustrative of the invention and impose no limits thereon not imposed by the appended claims, and in which:

Fig. 1 illustrates the first steps of extruding material about spaced conductors and drying the extruded material;

Fig. 2 illustrates the next step of baking the extruded material;

Fig. 3 illustrates the detector element after drying but before baking;

Fig. 4 is a sectional view taken on line 4--4 of Fig. 3;

Fig. 5 illustrates the detector element after the baking step;

Fig. 6 illustrates the detector element of Fig. 5 after enclosure in a protective tube; and

Fig. '7 is a sectional view taken on line 1-1 of Fig. 6.

In a preferred method of manufacturing a fire detector element in accordance with this invention, a thermistor material is used which will not deteriorate or be removed by heating within the range of temperatures including those to which the detector element is subjected in manufacture or use, and which will be fused to the metal of the conductors by heating. To this thermistor material is added material which will be removed, as by burning or volatilization. when heated to a temperature which may easily be producedv in manufacture and at which the thermistor material will fuse to the wires. This material is formed in a continuous cylinder about and beads may then be encased in a tightlyfltted metal casing which holds the parts permanently and firmly in position.

A material which has been found to be entirely satisfactory in carrying out the method of this invention has the following ingredients:

In forming this material the ingredients listed above are melted, poured into water and then ground to powder in a ball mill. Two or more parts of the powder are then mixed with ten parts by volume of a mixture of an inert ceramic material, such as steatite (60% to 90%), and a material which will be removed by heating, such as flour or other combustible material (40% to 10%), and after mixing in a ball mill sufficient water is added to make the mixture plastic. The flour or other combustible material constitutes the material which is removed by heating to cause the shrinkage which produces small units, designated beads, all as described hereinbefore. Sufficient of this material must be added to the thermistor frit to insure that when it is removed by heating the shrinkage will be enough to cause the desired separation into beads. The spacing of the beads is controlled by this shrinkage and must be great enough to allow bending of the finished detector cable through a small radius without breaking the wires or crushing the beads, but must also be small enough to prevent contact of the conductors with each other or with the protective casing. It has been found that the specified proportion of these ingredients will produce these results.

The described material is formed in a cylinder about two parallel, spaced electrically conductive wires. This step is preferably performed by extruding the material from a hopper 2 (see Fig. 1)

through an orifice 4 through which the conductors 5 are led, thus producing a solid cylinder of the material having the conductors embedded therein. This cylinder is led directly from the extruding orifice to a drying furnace It! the temperature in which may increase from 122 F. at the entrance to a maximum of 230 F. in a typical case. The purpose of this drying step is merely to impart an initial cohesiveness to the extruded material and permit further heating to remove the flour or similar material by oxidization, evaporation or sublimation without the generation of steam. The product of this drying step is illustrated in Figs. 3 and 4 and comprises a solid cylinder of thermistor material having the conductors 6 embedded therein. In accordance with the invention disclosed in my co-pending application, the tube is of elliptical cross-section with the conductors 6 lying in the major axis.

The dried solid cylinder 20, in the form shown in Fig. 3, and preferably in relatively long or continuous lengths, is now baked at a sufliciently high temperature for a sufficient length of time to cause the ceramic material to shrink into beads and become fused to the conductors. This step may be performed in any suitable heatin device,

such as the furnace 30 of Fig. 2, in which a plurality of elements 32 may be baked. In a process using the described materials, the heating is continued for approximately 48 hours at a temperature of approximately 1600 F. During this heat ing the extruded material 20 shrinks both radially and longitudinally of the wires, causing it to change from the continuous, cylindrical form shown in Fig. 3 to the form shown in Fig. 5, in which it comprises a plurality of beads 40 spaced along the conductors 6 and fused thereto and having the same elliptical cross-section as the continuous extruded material of Fig. 3. These beads will be slightly spaced apart or lightly abutting each other, at the centers thereof, as shown at 42 in Fig. 5 and will be spaced apart by progressively greater distances as the periphery is approached, being rounded at the periphery as the material fuses. Due to the fusing of the thermistor material to the conductors these parts are substantially permanently united, forming a unitary structure. The spacing of the beads permits the cable to be bent through a small angle, with the advantageous effects and results described hereinbefore.

After completion of the shrinking step the beads are allowed to cool and the entire assembly of beads and conductors is enclosed in a protective casing which may be made of suitable material, such as the alloys now known as Monel and Inconel, and which is of such small thickness (e. g. a few thousandths of an inch) that it does not prevent bending of the detector.

It will, of course, be apparent that other materials than those described hereinbefore may be used in carrying out the described process without departing in any way from the invention.

In another method of manufacture, for example, the material which is extruded about the ires is a mixture of one or more metallic organic compounds and some inert ceramic compound, such as steatite or aluminum oxide. The metallic organic compound dissociates on heating and the extruded material therefore shrinks to provide the beads resulting in the provision of a supporting matrix which incorporates with metallic oxides. Examples of metallic organic compounds are tetra ethyl lead Pb(C2H5)4, Sb(C2H5) 3, Ca(NHCsI-I5) 2, and others.

While I have described in this application a method comprising certain specified steps, it will be apparent to those skilled in the art that other steps may be added, or some of those disclosed may be eliminated, or those disclosed may be modified, all without departing in any way from the spirit or scope of the invention, for the limits of which reference must be had to the appended claims.

What is claimed is:

l. The method of manufacturing a continuous flexible cable comprising at least one wire and a plurality of beads of insulating material surrounding and fused thereto and spaced along the length thereof, which comprises the steps of forming about the wire a solid continuous cylinder of material containing an ingredient which is fused by heating and an ingredient which is removed by heating, and heating the assembly sufficiently to remove the heat-removable ingredient and fuse the fusible ingredient.

2. The method of manufacturing a device which comprises two spaced, parallel, continuous, electrically conductive wires and a plurality of beads surrounding and fused to the wires and spaced along the length thereof, which comprises the steps of forming about two spaced, parallel, continuous, electrically conductive wires a solid, continuous cylinder of material containing at least one ingredient which increases in electrical conductivity with temperature, which is not removed by heating within a. range within which the element is to be used and which will be fused to the conductors by heating, and at least one ingredient which will be removed by heating to the temperature required to fuse the first ingredient to the conductors, and heating the cylinder of material toremove the heat-removable ingredient and fuse the fusible ingredient.

3. The method of manufacturing a fire detector element or like device which comprises two spaced, parallel, continuous, electrically conductive wires and a plurality of beads surrounding and fused to the wires and spaced along the length thereof, which comprises the steps of forming about two spaced, parallel, continuous, electrically conductive wires a solid, continuous cylinder of material comprising an inert ceramic compound and a mixture of metallic organic compounds which dissociate and shrink on heating and the electrical conductivity of which increases with temperature, and heating said material to dissociate and shrink it into a plurality of beads spaced longitudinally along the length of the wire.

4. The method of manufacturing a continuous flexible cable comprising at least one wire and a plurality of beads of insulating material surrounding and adhered thereto and spaced along the length thereof, which comprises the steps of forming about the wire a solid continuous cylinder of material containing an ingredient which is fused by heating and an ingredient which is removed by heating, and heating the assembly sufiiciently to remove the heat-removable ingredient and fuse the fusible ingredient.

5. The method of manufacturing a temperature-sensitive resistance device comprising a plurality of spaced parallel electrically conductive wires and a plurality of beads of material the electrical resistance of which changes with changes in temperature surrounding and adhered to the wires and maintaining the wires in spaced relation, which comprises the steps of forming about parallel spaced wires a solid continuous cylinder of material containing an ingredient which is removed by heating, at least one ingredient which is not removed by such heating and the electrical resistance of which changes with changes in temperature, and a material which is fused by such heating, and heating to remove the removable ingredient and fuse the fusible ingredient, whereby the cylinder of material covering and spacing the wires shrinks longitudinally of the wires and separates at spaced point-s along the length thereof.

MELVILLE F. PETERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,332,348 MacDonald Mar. 2, 1920 2,091,107 Reichmann Aug. 24, 1937 2,149,002 Wermine Feb. 28, 1939 2,303,303 Schleicher Nov. 24, 1942 2,375,058 Wiegand May 1, 1945 

